Thickening of cortex areas implicated in mental illness shows increasing genetic influence as the brain develops in childhood and adolescence, NIMH researchers have found. These areas also happen to be the latest to evolve and the last to mature. The peak of genetic influence in these areas coincides with the typical age-of-onset of most mental disorders in late adolescence/early adulthood. The new findings may provide insight into the workings of gene-by-environment-by age interactions in the disorders, says Jay Giedd, M.D., of the NIMH Child Psychiatry Branch.